A number of different oligomerisation technologies are known to produce α-olefins. Some of these processes, including the Shell Higher Olefins Process and Ziegler-type technologies, have been summarized in WO 04/056479 A1. The same document also discloses that the prior art (e.g. WO 03/053891 and WO 02/04119) teaches that chromium based catalysts containing heteroaromatic ligands with both phosphorus and nitrogen heteroatoms, selectively catalyse the trimerisation of ethylene to 1-hexene.
Processes wherein transition metals and heteroatomic ligands are combined to form catalysts for trimerisation, tetramerisation, oligomerisation and polymerisation of olefinic compounds have also been described in different patent applications such as WO 03/053890 A1; WO 03/053891; WO 04/056479 A1; WO 04/056477 A1; WO 04/056480 A1; WO 04/056478 A1; U.S. Complete patent application Ser. No. 11/130,106; WO 05/123884 A2 and WO 05/123633 A1.
The catalysts utilized in the abovementioned trimerisation, tetramerisation, oligomerisation or polymerisation processes all include one or more catalyst activators to activate the catalyst. Such an activator is a compound that generates an active catalyst when the activator is combined with the catalyst.
Suitable activators include organoaluminium compounds, organoboron compounds, organic salts, such as methyl lithium and methyl magnesium bromide, inorganic acids and salts, such as tetrafluoroboric acid etherate, silver tetrafluoroborate, sodium hexafluoroantimonate and the like.
A common catalyst activator used in combination with Cr based catalysts for oligomerisation of olefinic compounds is alkylaluminoxane, particularly methylaluminoxane (MAO). It is well known that MAO includes significant quantities of alkylaluminium in the form of trimethylaluminium (TMA), and in effect the catalyst activator is a combination of TMA and MAO. The MAO may also be replaced with modified MAO (MMAO).
The use of fluorinated boranes/borates as catalyst activators is also known. In J Organomet. Chem. 683 (2003) 200 triazacyclohexane CrCl3 complexes were activated with AlR3 and [PhN(Me)2H]+[B(C6F5)4]− to give catalysts active for trimerisation of alpha-olefins. In J. Am. Chem. Soc., 126 (2004) 1304, Cr-based ethylene trimerisation catalysts were activated by treating Cr-aryl complexes with fluorinated aryl-boranes (BARF). IPCOM000031729D discloses the use of fluorinated borate and borane activators in combination with chromium based catalyst in the oligomerisation of olefins.
In WO 99/64476, catalysts (especially Ziegler-Natta and metallocene polymerisation catalysts) were activated by a combination of halogenated aryl containing Group13 metal or metalloid based Lewis acids and organo-Group13 metal compounds.
Trityl tetrakis(pentafluorophenoxo)aluminate, [Ph3C]+[Al(OC6F5)4]−, has been prepared and employed as a co-catalyst for ethylene and propylene polymerisation with metallocene complexes such as (C5H5)2ZrMe2 in Organometallics, 19 (2000) 1625 and Organometallics, 21 (2002) 3691. Angew. Chem. Int. Ed. 2004, 43, 2066 also discloses compounds such as [M(OC6F5)n] and [Al{OC(CF3)3}4]− and the use of the latter as an activator for ethene and propene polymerisation with a Zr-alkyl complex in the presence of AliBu3 J. Fluorine Chemistry 2001, 112, 83 discloses the preparation of compounds such as [Ph3C]+[Al{OC(CF3)3}4]−.
Journal of Organometallic Chemistry, 621 (2001), 184 discloses the use of [Me3NH]+[B(OC6F5)4]− for polymerisation with iron catalysts including tridentate ligands.
It has now been found that compounds of the present invention including at least one halogenated organic group bound to a group 3A or group 3B to 7B central atom by means of one or more binding atoms can be used as activators of oligomerisation catalysts in oligomerisation reactions. In some cases the productivity of the oligomerisation catalysts was found to have been improved compared to when borane or borate activators are used, such as those detailed in IPCOM000031729D. Most surprisingly it also has been found that different activators of this nature can influence the product selectivity of the oligomerisation catalysts. Furthermore, the relative high polymer formation associated with borate activators, was at least reduced in at least some cases.